(Levi) This isn't the lowest level you're thinking of. This is the hidden level. The level that houses the flooded mausoleum of Princess Celestia.....The mausoleum built for my mother....
(Levi) Well, immortal doesn't necessarily mean invincible. Immortal means that you'll never die of old age. That means that it's possible for you to be able to be killed even if you're immortal. In the case of my mom, she seemingly gave her life to save me from the Changelings, who would go on to be assimilated by the Dark Ponies. When I returned to the ruins of Canterlot, I couldn't find her or my aunt Luna. I ordered that this mausoleum be built, flooded, and then a fortress be built on top to conceal the Mausoleum's presence.
